This research seeks to discover what changes occur in the sensory periphery and the CNS during the evolutionary transition between deaf and hearing animals. Do new processing circuits arise specifically for hearing? Or are existing circuits modified somehow? What is the underlying mechanoreceptive CNS substrate for hearing? We propose to use an insect system as a model with which to answer these questions. The praying mantis is unique in possessing a single, ultrasound-sensitive ear in the ventral midline of the body, and the CNS terminations of the tympanal nerve are different from those in any other insect. Using both comparative (phylogenetic) and developmental (ontogenetic) strategies, we will trace the origins of the mantis auditory system, especially the central components, for comparison with other orthopteroid insects, both hearing and deaf. We will anatomically and neurophysiologically contrast hearing animals with primitively and secondarily deaf mantises, and also with species that have evolved a second, serially homologous ear. We will define nymphal changes in structure and function of the mantis ear. Immunohistochemical techniques will allow comparison of the embryological development of the mantis ear with that of a deaf outgroup, the cockroaches. The two parallel research paths will converge on the precursors of the mantis auditory system and the processes leading to audition.